Supplementary Figure Legends

Supplementary Figure 1 | Phylogenetic relationships of HA genes from H5N1 influenza viruses. Viruses used in this study are shown in color: human isolates in red and avian isolates in blue. The viruses were classified into 4 clades according to the published classification system (1).

Supplementary Figure 2 | Receptor specificity of H5N1 viruses. Direct binding activity to sialylglycopolymers containing either α2,3-linked (blue) or α2,6-linked (red) sialic acids was tested. a, Viruses isolated from avian species. b-d, Viruses isolated from humans or viruses generated by reverse genetics based on the HA sequences of human isolates in the Influenza Sequence Database. In all panels, the results are represented as means ±standard deviations of triplicate experiments.

Supplementary Figure 3 | Specificity of the receptor assay. Binding of (a) lectins and (b) viruses to sialylglycopolymers, asialoglycopolymers and polymer backbone. Sialylglycopolymers containing either α2,3-linked (blue) or α2,6-linked (red) sialic acids and the polymer lacking oligosaccharides (black) were treated (open circle) or mock-treated (closed circle) with Arthrobacter ureafaciens sialidase and then incubated with MALI, MALII, SNA lectin, or viruses, as indicated. The data are from a single representative experiment.

Supplementary Figure 4 | Effect of HA mutations on SAα2,6Gal recognition. Mutations found in the HA of A/Vietnam/30408/05clone7 were introduced individually or in combination into the reference VN1194 HA. Direct binding activity to sialylglycopolymers containing either α2,3-linked (blue) or α2,6-linked (red) sialic acids was tested. a, VN1194 HA and viruses with a single HA amino acid change. b, Viruses with two amino acid changes. c, Viruses with three amino acid changes and the A/Vietnam/30408/05clone7RG. Mutations introduced into the VN1194 HA are shown in parentheses. In all panels, the results are represented as means ±standard deviations of triplicate experiments.

Supplementary Reference1. World Health Organization Global Influenza Program Surveillance Network. Evolution

of H5N1 avian influenza viruses in Asia. Emerg. Infect. Dis. 11, 1515-1521 (2005).